AVS 57th International Symposium & Exhibition
    Surface Science Tuesday Sessions
       Session SS1-TuM

Invited Paper SS1-TuM3
Mechanisms of Catalytic Processes on Au: Imaging, Spectroscopy and Reactivity

Tuesday, October 19, 2010, 8:40 am, Room Picuris

Session: Catalysis on Metal and Alloy Surfaces
Presenter: C. Friend, Harvard University
Authors: C. Friend, Harvard University
Xu, Harvard University
Liu, Harvard University
Baker, Harvard University
Haubrich, Harvard University
R.J. Madix, Harvard University
Correspondent: Click to Email
The need for energy-efficient catalytic processes and the long fascination with Au as a material has spurred intense activity in the investigation of gold-based catalysis. There is on-going discussion of the origin of the activity of gold for oxidation reactions, including changes in the oxidation state and electronic properties of Au nanoparticles. We have demonstrated that atomic oxygen bound to Au is highly active for a range of oxidative transformations on metallic Au. Well-prepared gold crystal surfaces are inactive for O2 dissociation, so that ozone was used as an oxidant in order to probe the bonding and reactivity of O on Au. Oxidation of Au(111) leads to the release of Au nanoparticles on which O is adsorbed. A combination of scanning tunneling microscopy (STM), high resolution electron energy loss spectroscopy experiments complemented by density functional theory calculations show that the local bonding and degree of longer range order of the O-Au islands depends on the temperature of oxidation and the overall O coverage. Reactivity studies show that low coverages of O bound in sites of local three-fold coordination are most active for selective reactions. Investigations of the molecular-scale mechanism for oxidative coupling reactions promoted by atomic oxygen on Au will be presented. Oxidative coupling of oxygenates—alcohols and aldehydes—will be the focus of the talk. The coupling reactions yield organic esters, which are important products industrially because of their widespread use as precursors for fragrances, flavorings, and fabrics. We construct a general mechanism for this class of reactions that provides insight into the optimum conditions of selectivity for even complex mixtures of alcohols. These fundamental studies will also be related to parallel studies using nanoporous Au as a catalyst at atmospheric pressure to illustrate the value of fundamental studies of catalytic processes. In this case, the reactions of Au under ultrahigh vacuum conditions provide an understanding of reactions at higher pressure because of the low intrinsic reactivity of Au itself, the weak bonding of water to Au, and the low steady state concentration of reactants on the surface even at high pressure because of the low rate of O2 dissociation on Au. This is an unprecedented success in bridging the pressure gap between fundamental studies and working catalytic conditions.